* Allow Slot::setVariant() to work on PyrObject*.
* Use QObjectProxy::invokeScMethod() in QcFunctionSignalHandler
* Move the essence of QObjectProxy::invokeScMethod() out into the
new global QtCollider::runLang().

This allows deleting of objects without the need to lock the language,
in turn allowing to delete objects from within the language itself.
- Make QObjectProxy alive for the lifetime of its SC object.
- Only QObjectProxy* can now safely be passed from SC to Qt thread,
so adjust Slot interface accordingly.
- Check whether the Qt object pointed to by proxy is alive before
using it.
- Fail primitives if object not alive
- Store every constructed QObject[SC] into QObject.heap array for the
lifetime of target QObject[Qt]
- Implement new QObject.isValid; not very useful, as even after it
returns true, the object might be destroyed.
A better alternative yet to be found!
- evaluate QView.onClose in response to Qt object's destroyed() signal